#!/usr/bin/env python3
#
# Copyright (C) 2024 VyOS maintainers and contributors
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License version 2 or later as
# published by the Free Software Foundation.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.

import ipaddress
import jmespath
import logging
import os

from sys import exit
from logging.handlers import SysLogHandler

from vyos.config import Config
from vyos.configdict import is_node_changed
from vyos.template import render
from vyos.utils.process import cmd
from vyos.utils.process import run
from vyos import ConfigError
from vyos import airbag

airbag.enable()


nftables_cgnat_config = '/run/nftables-cgnat.nft'

# Logging
logger = logging.getLogger('cgnat')
logger.setLevel(logging.DEBUG)

syslog_handler = SysLogHandler(address="/dev/log")
syslog_handler.setLevel(logging.INFO)

formatter = logging.Formatter('%(name)s: %(message)s')
syslog_handler.setFormatter(formatter)

logger.addHandler(syslog_handler)


class IPOperations:
    def __init__(self, ip_prefix: str):
        self.ip_prefix = ip_prefix
        self.ip_network = ipaddress.ip_network(ip_prefix) if '/' in ip_prefix else None

    def get_ips_count(self) -> int:
        """Returns the number of IPs in a prefix or range.

        Example:
        % ip = IPOperations('192.0.2.0/30')
        % ip.get_ips_count()
        4
        % ip = IPOperations('192.0.2.0-192.0.2.2')
        % ip.get_ips_count()
        3
        """
        if '-' in self.ip_prefix:
            start_ip, end_ip = self.ip_prefix.split('-')
            start_ip = ipaddress.ip_address(start_ip)
            end_ip = ipaddress.ip_address(end_ip)
            return int(end_ip) - int(start_ip) + 1
        elif '/31' in self.ip_prefix:
            return 2
        elif '/32' in self.ip_prefix:
            return 1
        else:
            return sum(
                1
                for _ in [self.ip_network.network_address]
                + list(self.ip_network.hosts())
                + [self.ip_network.broadcast_address]
            )

    def convert_prefix_to_list_ips(self) -> list:
        """Converts a prefix or IP range to a list of IPs including the network and broadcast addresses.

        Example:
        % ip = IPOperations('192.0.2.0/30')
        % ip.convert_prefix_to_list_ips()
        ['192.0.2.0', '192.0.2.1', '192.0.2.2', '192.0.2.3']
        %
        % ip = IPOperations('192.0.0.1-192.0.2.5')
        % ip.convert_prefix_to_list_ips()
        ['192.0.2.1', '192.0.2.2', '192.0.2.3', '192.0.2.4', '192.0.2.5']
        """
        if '-' in self.ip_prefix:
            start_ip, end_ip = self.ip_prefix.split('-')
            start_ip = ipaddress.ip_address(start_ip)
            end_ip = ipaddress.ip_address(end_ip)
            return [
                str(ipaddress.ip_address(ip))
                for ip in range(int(start_ip), int(end_ip) + 1)
            ]
        elif '/31' in self.ip_prefix:
            return [
                str(ip)
                for ip in [
                    self.ip_network.network_address,
                    self.ip_network.broadcast_address,
                ]
            ]
        elif '/32' in self.ip_prefix:
            return [str(self.ip_network.network_address)]
        else:
            return [
                str(ip)
                for ip in [self.ip_network.network_address]
                + list(self.ip_network.hosts())
                + [self.ip_network.broadcast_address]
            ]

    def get_prefix_by_ip_range(self):
        """Return the common prefix for the address range

        Example:
            % ip = IPOperations('100.64.0.1-100.64.0.5')
            % ip.get_prefix_by_ip_range()
            100.64.0.0/29
        """
        if '-' in self.ip_prefix:
            ip_start, ip_end = self.ip_prefix.split('-')
            start_ip = ipaddress.IPv4Address(ip_start.strip())
            end_ip = ipaddress.IPv4Address(ip_end.strip())

            start_int = int(start_ip)
            end_int = int(end_ip)

            # XOR to find differing bits
            xor = start_int ^ end_int

            # Count the number of leading zeros in the XOR result to find the prefix length
            prefix_length = 32 - xor.bit_length()

            # Calculate the network address
            network_int = start_int & (0xFFFFFFFF << (32 - prefix_length))
            network_address = ipaddress.IPv4Address(network_int)

            return f"{network_address}/{prefix_length}"
        return self.ip_prefix


def _delete_conntrack_entries(source_prefixes: list) -> None:
    """Delete all conntrack entries for the list of prefixes"""
    for source_prefix in source_prefixes:
        run(f'conntrack -D -s {source_prefix}')


def generate_port_rules(
    external_hosts: list,
    internal_hosts: list,
    port_count: int,
    global_port_range: str = '1024-65535',
) -> list:
    """Generates a list of nftables option rules for the batch file.

    Args:
        external_hosts (list): A list of external host IPs.
        internal_hosts (list): A list of internal host IPs.
        port_count (int): The number of ports required per host.
        global_port_range (str): The global port range to be used. Default is '1024-65535'.

    Returns:
        list: A list containing two elements:
            - proto_map_elements (list): A list of proto map elements.
            - other_map_elements (list): A list of other map elements.
    """
    rules = []
    proto_map_elements = []
    other_map_elements = []
    start_port, end_port = map(int, global_port_range.split('-'))
    total_possible_ports = (end_port - start_port) + 1

    # Calculate the required number of ports per host
    required_ports_per_host = port_count
    current_port = start_port
    current_external_index = 0

    for internal_host in internal_hosts:
        external_host = external_hosts[current_external_index]
        next_end_port = current_port + required_ports_per_host - 1

        # If the port range exceeds the end_port, move to the next external host
        while next_end_port > end_port:
            current_external_index = (current_external_index + 1) % len(external_hosts)
            external_host = external_hosts[current_external_index]
            current_port = start_port
            next_end_port = current_port + required_ports_per_host - 1

        proto_map_elements.append(
            f'{internal_host} : {external_host} . {current_port}-{next_end_port}'
        )
        other_map_elements.append(f'{internal_host} : {external_host}')

        current_port = next_end_port + 1
        if current_port > end_port:
            current_port = start_port
            current_external_index += 1  # Move to the next external host

    return [proto_map_elements, other_map_elements]


def get_config(config=None):
    if config:
        conf = config
    else:
        conf = Config()

    base = ['nat', 'cgnat']
    config = conf.get_config_dict(
        base,
        get_first_key=True,
        key_mangling=('-', '_'),
        no_tag_node_value_mangle=True,
        with_recursive_defaults=True,
    )

    if conf.exists(base) and is_node_changed(conf, base + ['pool']):
        config.update({'delete_conntrack_entries': {}})

    return config


def verify(config):
    # bail out early - looks like removal from running config
    if not config:
        return None

    if 'pool' not in config:
        raise ConfigError(f'Pool must be defined!')
    if 'rule' not in config:
        raise ConfigError(f'Rule must be defined!')

    for pool in ('external', 'internal'):
        if pool not in config['pool']:
            raise ConfigError(f'{pool} pool must be defined!')
        for pool_name, pool_config in config['pool'][pool].items():
            if 'range' not in pool_config:
                raise ConfigError(
                    f'Range for "{pool} pool {pool_name}" must be defined!'
                )

    external_pools_query = "keys(pool.external)"
    external_pools: list = jmespath.search(external_pools_query, config)
    internal_pools_query = "keys(pool.internal)"
    internal_pools: list = jmespath.search(internal_pools_query, config)

    used_external_pools = {}
    used_internal_pools = {}
    for rule, rule_config in config['rule'].items():
        if 'source' not in rule_config:
            raise ConfigError(f'Rule "{rule}" source pool must be defined!')
        if 'pool' not in rule_config['source']:
            raise ConfigError(f'Rule "{rule}" source pool must be defined!')

        if 'translation' not in rule_config:
            raise ConfigError(f'Rule "{rule}" translation pool must be defined!')

        # Check if pool exists
        internal_pool = rule_config['source']['pool']
        if internal_pool not in internal_pools:
            raise ConfigError(f'Internal pool "{internal_pool}" does not exist!')
        external_pool = rule_config['translation']['pool']
        if external_pool not in external_pools:
            raise ConfigError(f'External pool "{external_pool}" does not exist!')

        # Check pool duplication in different rules
        if external_pool in used_external_pools:
            raise ConfigError(
                f'External pool "{external_pool}" is already used in rule '
                f'{used_external_pools[external_pool]} and cannot be used in '
                f'rule {rule}!'
            )

        if internal_pool in used_internal_pools:
            raise ConfigError(
                f'Internal pool "{internal_pool}" is already used in rule '
                f'{used_internal_pools[internal_pool]} and cannot be used in '
                f'rule {rule}!'
            )

        used_external_pools[external_pool] = rule
        used_internal_pools[internal_pool] = rule

        # Check calculation for allocation
        external_port_range: str = config['pool']['external'][external_pool]['external_port_range']

        external_ip_ranges: list = list(
            config['pool']['external'][external_pool]['range']
        )
        internal_ip_ranges: list = config['pool']['internal'][internal_pool]['range']
        start_port, end_port = map(int, external_port_range.split('-'))
        ports_per_range_count: int = (end_port - start_port) + 1

        external_list_hosts_count = []
        external_list_hosts = []
        internal_list_hosts_count = []
        internal_list_hosts = []
        for ext_range in external_ip_ranges:
            # External hosts count
            e_count = IPOperations(ext_range).get_ips_count()
            external_list_hosts_count.append(e_count)
            # External hosts list
            e_hosts = IPOperations(ext_range).convert_prefix_to_list_ips()
            external_list_hosts.extend(e_hosts)
        for int_range in internal_ip_ranges:
            # Internal hosts count
            i_count = IPOperations(int_range).get_ips_count()
            internal_list_hosts_count.append(i_count)
            # Internal hosts list
            i_hosts = IPOperations(int_range).convert_prefix_to_list_ips()
            internal_list_hosts.extend(i_hosts)

        external_host_count = sum(external_list_hosts_count)
        internal_host_count = sum(internal_list_hosts_count)
        ports_per_user: int = int(
            config['pool']['external'][external_pool]['per_user_limit']['port']
        )
        users_per_extip = ports_per_range_count // ports_per_user
        max_users = users_per_extip * external_host_count

        if internal_host_count > max_users:
            raise ConfigError(
                f'Rule "{rule}" does not have enough ports available for the '
                f'specified parameters'
            )


def generate(config):
    if not config:
        return None

    proto_maps = []
    other_maps = []

    for rule, rule_config in config['rule'].items():
        ext_pool_name: str = rule_config['translation']['pool']
        int_pool_name: str = rule_config['source']['pool']

        # Sort the external ranges by sequence
        external_ranges: list = sorted(
            config['pool']['external'][ext_pool_name]['range'],
            key=lambda r: int(config['pool']['external'][ext_pool_name]['range'][r].get('seq', 999999))
        )
        internal_ranges: list = [range for range in config['pool']['internal'][int_pool_name]['range']]
        external_list_hosts_count = []
        external_list_hosts = []
        internal_list_hosts_count = []
        internal_list_hosts = []

        for ext_range in external_ranges:
            # External hosts count
            e_count = IPOperations(ext_range).get_ips_count()
            external_list_hosts_count.append(e_count)
            # External hosts list
            e_hosts = IPOperations(ext_range).convert_prefix_to_list_ips()
            external_list_hosts.extend(e_hosts)

        for int_range in internal_ranges:
            # Internal hosts count
            i_count = IPOperations(int_range).get_ips_count()
            internal_list_hosts_count.append(i_count)
            # Internal hosts list
            i_hosts = IPOperations(int_range).convert_prefix_to_list_ips()
            internal_list_hosts.extend(i_hosts)

        external_host_count = sum(external_list_hosts_count)
        internal_host_count = sum(internal_list_hosts_count)
        ports_per_user = int(
            jmespath.search(f'pool.external."{ext_pool_name}".per_user_limit.port', config)
        )
        external_port_range: str = jmespath.search(
            f'pool.external."{ext_pool_name}".external_port_range', config
        )

        rule_proto_maps, rule_other_maps = generate_port_rules(
            external_list_hosts, internal_list_hosts, ports_per_user, external_port_range
        )

        proto_maps.extend(rule_proto_maps)
        other_maps.extend(rule_other_maps)

    config['proto_map_elements'] = ', '.join(proto_maps)
    config['other_map_elements'] = ', '.join(other_maps)

    render(nftables_cgnat_config, 'firewall/nftables-cgnat.j2', config)

    # dry-run newly generated configuration
    tmp = run(f'nft --check --file {nftables_cgnat_config}')
    if tmp > 0:
        raise ConfigError('Configuration file errors encountered!')


def apply(config):
    if not config:
        # Cleanup cgnat
        cmd('nft delete table ip cgnat')
        if os.path.isfile(nftables_cgnat_config):
            os.unlink(nftables_cgnat_config)
        return None
    cmd(f'nft --file {nftables_cgnat_config}')

    # Logging allocations
    if 'log_allocation' in config:
        allocations = config['proto_map_elements']
        allocations = allocations.split(',')
        for allocation in allocations:
            try:
                # Split based on the delimiters used in the nft data format
                internal_host, rest = allocation.split(' : ')
                external_host, port_range = rest.split(' . ')
                # Log the parsed data
                logger.info(
                    f"Internal host: {internal_host.lstrip()}, external host: {external_host}, Port range: {port_range}")
            except ValueError as e:
                # Log error message
                logger.error(f"Error processing line '{allocation}': {e}")

    # Delete conntrack entries
    if 'delete_conntrack_entries' in config:
        internal_pool_prefix_list = []
        for rule, rule_config in config['rule'].items():
            internal_pool = rule_config['source']['pool']
            internal_ip_ranges: list = config['pool']['internal'][internal_pool]['range']
            for internal_range in internal_ip_ranges:
                ip_prefix = IPOperations(internal_range).get_prefix_by_ip_range()
                internal_pool_prefix_list.append(ip_prefix)
        # Deleta required sources for conntrack
        _delete_conntrack_entries(internal_pool_prefix_list)


if __name__ == '__main__':
    try:
        c = get_config()
        verify(c)
        generate(c)
        apply(c)
    except ConfigError as e:
        print(e)
        exit(1)